Expand and combine like terms. $(2x^4+3x^3)(2x^4-3x^3)=$
We can expand this expression like any product of two binomials. However, this expression has a special form that makes it easier to expand. This is the "difference of squares" form (where $P$ and $Q$ can be any monomial): $(P+Q)(P-Q)=P^2-Q^2$ $\begin{aligned} &\phantom{=}(2x^4+3x^3)(2x^4-3x^3) \\\\ &=\left(2x^4\right)^2-\left(3x^3\right)^2 \\\\ &=4x^8-9x^6 \end{aligned}$